1. Field of the Invention
The present invention relates to a ceramic device which is usable as a passive device, an active device, and a sensor device. The passive device includes, for example, various transducers, various actuators, frequency region functional parts (filters), and transformers. The active device includes, for example, vibrators, resonators, oscillators, and discriminators for the communication and the power generation. The sensor device includes, for example, ultrasonic sensors, acceleration sensors, angular velocity sensors, shock sensors, and mass sensors.
2. Description of the Related Art
Nowadays, a displacement device which adjusts the optical path length and the position to the submicron order is used in the fields of the optics and the precision machining, for example. The displacement device includes an actuator utilizing the inverse piezoelectric effect caused when an electric field is applied to a piezoelectric/electrostrictive material.
As for the actuator, the present applicant has already proposed a piezoelectric/electrostrictive film type device made of ceramics which is used for various purposes, for example, as described in Japanese Laid-Open Patent Publication Nos. 3-128681 and 5-49270.
The piezoelectric/electrostrictive film type device is a compact, inexpensive, and highly reliable electromechanical conversion device. Further, large displacement is obtained at a low driving voltage. The piezoelectric/electrostrictive film type device also has excellent features such that response is quick and generated force is large. Therefore, the piezoelectric/electrostrictive film type device is useful as a component of actuators, display devices, relays, or the like.
The piezoelectric/electrostrictive film type device is mechanically displaced in accordance with inverse piezoelectric effect or electrostrictive effect by applying a voltage to an operating section (actuator element). Accordingly, when it is intended to displace the operating section upwardly and downwardly at a constant amplitude, a pulse voltage having a constant amplitude may be applied thereto.
However, when driving durability was practically examined for the operating section as described above, it was confirmed that the decrease in displacement amount (deterioration of the displacement) was caused in an extremely short period if a coating made of resin or the like was applied to the surface of the operating section as a load to suppress the displacement action. This phenomenon was not observed when the operating section was examined singly.